The present invention relates to an aircraft turbojet comprising a system for bleeding air from said turbojet, an aircraft comprising at least one such turbojet, and a method for controlling such a turbojet.
FIG. 1 shows an aircraft bypass turbojet 10 equipped with a prior art bleeding system 100 that is intended to bleed air in the turbojet 10 and to deliver said air to an air system 60, such as the conditioned air system 60 of the aircraft cabin.
The turbojet 10 comprises:                a fan 12 intended to generate a flow of air in the turbojet 10 in a direction of displacement 50 of air in the turbojet, in which case, as is known, the flow of air then moves downstream of the fan in a primary vein of the turbojet 10 or in a secondary vein thereof,        a compressor 14 that comprises a low-pressure compressor 16 downstream of the fan 12 and a high-pressure compressor 18 arranged downstream of the low-pressure compressor 16,        a turbine 20 that comprises a high-pressure turbine 22 downstream of the high-pressure compressor 18 and a low-pressure turbine 24 downstream of the high-pressure turbine 22.        
The air pushed by the fan and traveling in the primary vein then passes in succession through the low-pressure compressor 16, the high-pressure compressor 18, the high-pressure turbine 22, and the low-pressure turbine 24 so as to be ejected to the outside.
Between the high-pressure compressor 18 and the high-pressure turbine 22, the air passes through a combustion chamber 26.
The high-pressure compressor 18 comprises a plurality of compression stages in which the pressure rises, from upstream to downstream in the direction of displacement 50, from a low pressure at the first stage to a high pressure at the last stage, passing through an intermediate pressure in the vicinity of the middle stage.
The bleeding system 100 comprises:                a first air intake 102 intended to bleed the air at the intermediate pressure in the high-pressure compressor 18,        a second air intake 104 intended to bleed the air at high pressure in the high-pressure compressor 18,        a check valve 106 fluidically connected to the first air intake 102 that prevents the air from moving toward said first air intake 102,        a high-pressure valve 108 fluidically connected to the second air intake 104 and controlled so as to be open or closed alternatively,        a control valve 110 intended to control the pressure of the flow of air passing therethrough, the outlet of the high-pressure valve 108 and the outlet of the check valve 106 being fluidically connected to the same inlet of the control valve 110,        a cooler 112 intended to cool the air passing therethrough, the outlet of the control valve 110 being fluidically connected to an inlet of the cooler 112 and an outlet of the cooler 112 being fluidically connection to the air system 60 of the aircraft,        a controller 114 intended to control the high-pressure valve 108 and the control valve 110.        
The air necessary for the cooling performed in the cooler 112 is bled through a system of pipes 116 arranged downstream of the fan 12 in the secondary air vein of the turbojet 10.
The air pressure at the outlet of the cooler 112 must be compatible with the air pressure that must be injected in the air system 60. In the case of a pressurized cabin, the air pressure typically must be between 137895.14 Pa (20 psia) and 206842.72 Pa (30 psia).
Thus, when the pressure at the first air intake 102 is above a first threshold, typically 275790.29 Pa (40 psia), the air necessary for operation of the bleeding system 100 is bled at the first air intake 102, and when the pressure in the bleeding system 100 is below a second threshold, typically 206842.72 Pa (30 psia), the air necessary for operation of the bleeding system 100 is bled at the second air intake 104.
To this end, a pressure sensor measures the value of the pressure at the first air intake 102 and another pressure sensor 111 measures the value of the pressure in the bleeding system 100. Such a pressure sensor 111 is installed, for example, downstream of the junction between the outlet of the check valve 106 and the outlet of the high-pressure valve 108.
The bleeding system 100 then operates as follows:                when the pressure at the first air intake 102 is above a first threshold, the controller 114 orders the closure of the high-pressure valve 108,        the air is then bled at the first air intake 102, passes through the check valve 106 and supplies the control valve 110,        when the pressure in the bleeding system 100 is below the second threshold, the controller 114 orders the opening of the high-pressure valve 108,        the air is then bled at the second air intake 104, passes through the high-pressure valve 108 and supplies the control valve 110, and the check valve 106 prevents the air from returning to the turbojet 10,        the controller 114 controls the control valve 110 in accordance with the air pressure that is to be obtained,        the air at the outlet of the control valve 110 passes through the cooler 112, then supplies the air system 60.        
Such a layout is not always satisfactory in terms of energy consumption.